There is a bigger difference than just monthly payment on an arm vs 30yr fix. You will have to deal with the adjustment and prossibly will not be able to refinance out of it in the given time frame depending on what you put down. An adjusment on a 700/800K loan is well over 1K.
Also, I think advice from people that do not have a financial interest in your decison is not a bad idea… Don’t ya think?